The present invention relates generally to vehicular diagnostic systems and particularly to a computer interface apparatus for communicating between the on-board vehicle computer system and a computer equipped test head.
With the advent of motor vehicles being equipped with computer control systems by the manufacturer, the repair of malfunctions has become substantially more sophisticated than in the past. In order for the vehicle computer to properly perform its control functions, it typically interrogates a variety of sensors which are used to monitor various vehicle operating parameters. In several of these vehicle computer systems, as many as twenty or more sensors are employed for control purposes and to assist on-board diagnosis by the vehicle computer, so that an immediate warning may be displayed to the vehicle operator.
Additionally, some vehicle computer systems employ several separate microprocessor-based computer devices which cooperate with one another in providing the vehicle control functions. By the year 1987, it is expected that the vehicular computer system will comprise on the order of ten or eleven separate microprocessor-based computers. Through multiplexing techniques, these separate computers, and their associated sensors and actuators, will communicate via a single serial data bus implemented using a simple three-wire circuit (common, 12 volt and ground) within the vehicle. Through such multiplexing techniques the complex wiring harnesses found on most present day vehicles, and the attendant circuit tracing and trouble shooting problems, are expected to be all but eliminated.
To some extent the foregoing multiplexing techniques have already been utilized in todays vehicles, primarily in communicating between the vehicle computer system and its sensors. Communication is performed by transmitting digital data in a serial format, typically at a baud rate of 160, i.e., approximately 16 characters per second.
In many vehicle models, there is provided a means for obtaining direct access to the monitored parameter data, on a real time basis, so that various display tools, engine analyzers and so forth may be used to facilitate a more complete diagnosis than that provided by the on-board vehicle computer. For example, in many General Motors vehicle models, an Assembly Line Communication Link (ALCL) terminal is installed under the dashboard of the vehicle in the passenger compartment. This ALCL terminal is connected to an input/output (IO) port of the vehicle computer or to an electronic control module (EOM), to permit the transmission of monitored parameter data to the ALCL terminal upon reception of the appropriate data enable signal at the ALCL terminal.
In the past, hand-held display tools have been employed to selectively display the value or status of individual parameters. For a further discussion of such hand-held display tools, reference may be had to commonly assigned patent U.S. Pat. No. 4,602,127, entitled "Diagnostic Data Recorder", by James F. Neely and James E. Krass, Jr., filed Mar. 9, 1984, which patent is hereby incorporated by reference. As noted above, present day vehicle computer systems communicate parameter data serially at a baud rate of 160. At such baud rates, hand-held display tools are generally useful. However, with the prospect of much greater use of computers in future vehicle models, it becomes apparent that hand-held display tools will be inadequate. First, with a large number of individual computers all competing for use of the serial data bus (three-wire conductor) the data communication baud rate must be increased significantly. In fact, large General Motors trucks already operate at a baud rate of 9600, and many passenger vehicles are soon expected to employ computer systems communicating at a baud rate of 8192. Present day hand-held display tools are not well adapted to receiving data at such baud rates. Second, with the increase in baud rate and increase in the number of on-board computers and sensors, there comes a very substantial increase in the volume of data which must be analyzed. To perform a full and complete analysis of such highly computer intensive vehicles would require far too many switches, knobs and light emitting displays to be practical.
Additionally, it should be appreciated that as the analysis of the vehicular data becomes more sophisticated, the computer programs developed to carry out the analysis will become very complex. Yet, with each new model year, the format of the data being transmitted from the on-board computer is subject to change. In order to minimize the changes in the complex diagnostic computer program, it would be desirable to provide an interface between the on-board vehicle computer and the off-board test computer which could adapt to variations in the baud rates and types of data streams being generated by different vehicular computers. Thus, there is a need for a communications adapter circuit which is capable of receiving data from a wide variety of on-board vehicular computers and transforming these varied data streams from car to car into a standard format which would be readily accepted by the test computer.
Accordingly, consistent with the rapidly expanding use of on-board computer systems, there is a corresponding need for test equipment which is capable of analyzing all facets of the vehicle's operation, including the on-board computer operation.
It is, therefore, a principle objective of the present invention to provide a communications adapter apparatus which will facilitate communications between the on-board computer system of an automotive vehicle and a test and a test computer used to analyze the data transmitted from the on-board computer.
It is another objective of the present invention to provide a communications adaptor apparatus which is capable of transmitting commands to an on-board computer vehicle system as well as receiving data from the vehicle computer system.
It is yet another objective of the present invention to provide a communications adapter apparatus for coupling the on-board vehicle computer system with an outboard system, such as a microcomputer system, to permit diagnostic tests to be performed on a real time basis with vehicle operation.
It is yet a further objective of the present invention to provide a communications adapter apparatus in the form of a circuit board capable of being directly connected to the control bus, data bus, and address bus of an outboard microcomputer.
It is an additional objective of the present invention to provide a communications adapter apparatus which is capable of receiving a wide variety of data streams and baud rates.
It is a further objective of the present invention to provide a communications adapter apparatus which is capable of performing a self diagnosis on the vehicle interface.
It is still another objective of the present invention to provide a communications adapter circuit which is capable of depositing data directly into the memory map of the test computer.
It is still a further objective of the present invention to provide a communications adapter circuit whose control program may be readily updated to adjust for future changes in vehicle computers.
To achieve the foregoing objectives, the present invention provides a communications adapter circuit for permitting data communications at variable baud rates between an on-board vehicle computer and a test computer which is programmed to analyze data received from the on-board vehicle computer. The adapter comprises a first interface means for transmitting at least one command from the communications adapter circuit to the on-board vehicle computer. The interface means is adapted for receiving a stream of data from the on-board vehicle computer in response to the command. The adapter further comprises a second interface means for permitting the communications adapter circuit to share the bus structure of the test computer. A dual-ported memory connected to the first and second interface circuits is provided for storing data received from the on-board vehicle computer and for enabling a direct transfer of the stored data to the data bus of the test computer. An addressing control means connected to the dual-ported memory is provided for assigning the dual-ported memory a range of address locations in the memory map of the test computer.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.